1. Technical Field
The present disclosure relates to printed circuit boards, and more particularly to a printed circuit board eliminating voltage noise.
2. Description of Related Art
To accommodate miniaturization and power conservation, operating voltages of electronic devices are increasingly being reduced. However, lowering the operating voltage result in the electronic devices being more vulnerable to spurious noise. For current technology, once the operating voltage of the electronic device exceeds a threshold value, most electronic devices stops function, so it is necessary to add a filter circuit to eliminate voltage noise.
Referring to FIGS. 1 and 2, a low pass filter circuit 100 is shown. The low pass filter circuit 100 includes an inductor L and a capacitor C. A first terminal of the inductor L functions as an input terminal 10 of the low pass filter circuit 100 receiving direct current (DC) voltage, a second terminal of the inductor L is grounded via the capacitor C and functions as an output terminal 20 of the low pass filter circuit 100 to output the DC to an electronic device. Inductance of the inductor L and capacitance of the capacitor C maintain constant, in order to test the amplitude-frequency characteristic of the low pass filter circuit 100, an alternating current (AC) signal generator Vs is connected to the input terminal 10 to act as a noise source, a load resistor RL is connected to the output terminal 20, and an oscillograph may be connected to the output terminal 20 to detect amplitude-frequency characteristics.
Referring to FIG. 3, The AC signal generator Vs outputs an AC signal with an amplitude value M. A frequency of the AC signal gradually increases from zero hertzs (Hz). When the frequency of the AC signal falls below a frequency f1, the voltage amplitude of the output terminal 20 substantially equals the amplitude value M. When the frequency of the AC signal gradually increases from frequency f1 to f2, the voltage amplitude of the output terminal 20 gradually increases to a highest amplitude value N at the frequency f2. When the frequency of the AC signal increases from f2, the voltage amplitude of the output terminal 20 decreases. The low pass filter circuit 100 effectively amplifies the noise at the frequency f2, which can severely damage the electronic device.